1. Field of the Invention
The present invention relates to a fundus oculi observation device for observing a fundus oculi, and a fundus oculi image processing device for processing a fundus oculi image.
2. Description of the Related Art
As a fundus oculi observation device, a retinal camera has been widely used conventionally. FIG. 15 shows an example of the appearance of a general retinal camera used conventionally. FIG. 16 shows an example of the configuration of an optical system internally accommodated in the retinal camera (refer to Japanese Unexamined Patent Application Publication No. 2004-350849, for example). Herein, “observation” includes at least a case of observing a photographed fundus oculi image (observation of a fundus oculi with a naked eye may be included).
First, referring to FIG. 15, the appearance of a conventional retinal camera 1000 will be described. This retinal camera 1000 is provided with a platform 3 mounted on a base 2 so as to be slidable in the front and rear, right and left directions (horizontal directions). On this platform 3, an operation panel 3a and a control lever 4 for an examiner to perform various operations are mounted.
The examiner can freely move the platform 3 on the base 2 by operating the control lever 4. On the top of the control lever 4, an operation button 4a pressed down for requiring execution of production of a fundus oculi image is mounted.
On the base 2, a post 5 is mounted standing upward. This post 5 is provided with a jaw rest 6 where a jaw of a subject is rested, and an external fixation lamp 7 serving as a light source for fixing an eye E.
On the platform 3, a main body part 8 is placed for accommodating various optical systems and control systems of the retinal camera 1000. The control system may be placed, for example, inside the base 2 or the platform 3, or in an external device such as a computer connected to the retinal camera 1000.
On the side of the eye E of the main body part 8, an objective lens part 8a placed facing the eye E is disposed. On the examiner's side, an eyepiece part 8b is disposed.
Further, to the main body part 8, a still camera 9 for producing a still image of the fundus oculi of the eye E and an imaging device 10 such as a TV camera for producing a still image or moving image of the fundus oculi are connected. The still camera 9 and the imaging device 10 are formed so as to be removable from the main body part 8.
As the still camera 9, in accordance with various conditions such as the purpose of an examination and a method of saving a photographed image, a digital camera equipped with a CCD, a film camera, an instant camera and the like may be interchangeably used as necessary. The main body part 8 is provided with a mounting part 8c for interchangeably mounting the still camera 9.
In a case where the still camera 9 and the imaging device 10 are of digital imaging type, it is possible to transmit and store image data into an image recording device such as a computer connected to the retinal camera 1000.
Furthermore, on the examiner's side of the main body part 8, a touch panel monitor 11 is disposed. On this touch panel monitor 11, a fundus oculi image of the eye E formed based on video signals outputted from the (digital-type) still camera 9 or imaging device 10 is displayed. Moreover, on the touch panel monitor 11, an x-y coordinate system taking the center of a screen as the origin is displayed superimposed on the fundus oculi image. When the examiner touches the screen, coordinate values corresponding to a touched position are displayed.
Next, referring to FIG. 16, the configuration of the optical system of the retinal camera 1000 will be described. The retinal camera 1000 is provided with an illumination optical system 100 that illuminates a fundus oculi Ef of the eye E, and an imaging optical system 120 that guides the illumination light reflected by the fundus oculi to the eyepiece part 8b, the still camera 9 and the imaging device 10.
The illumination optical system 100 comprises: a halogen lamp 101; a condenser lens 102; a xenon lamp 103; a condenser lens 104; exciter filters 105 and 106; a ring transparent plate 107; a mirror 108; an LCD 109; an illumination diaphragm 110; a relay lens 111; an aperture mirror 112; and an objective lens 113.
The halogen lamp 101 is an observation light source that emits continuous light. The condenser lens 102 is an optical element for converging the continuous light (observation illumination light) emitted by the halogen lamp 101 and evenly applying the observation illumination light to the eye E (fundus oculi Ef).
The xenon lamp 103 is an imaging light source that is flashed at the time of imaging of the fundus oculi Ef. The condenser lens 104 is an optical element for converging the flash light (imaging illumination light) emitted by the xenon lamp 103 and evenly applying the imaging illumination light to the fundus oculi Ef.
The exciter filters 105 and 106 are filters used at the time of fluorography of an image of the fundus oculi Ef. The exciter filters 105 and 106 can be respectively inserted into and removed from an optical path by a drive mechanism such as a solenoid. The exciter filter 105 is placed on the optical path at the time of FAG (fluorescein angiography). The exciter filter 106 is placed on the optical path at the time of ICG (indocyanine green angiography). At the time of color-imaging, both the exciter filters 105 and 106 are retracted from the optical path.
The ring transparent plate 107 is placed in a conjugating position with a pupil of the eye E, and is provided with a ring transparent part 107a taking the optical axis of the illumination optical system 100 as the center. The mirror 108 reflects the illumination light emitted by the halogen lamp 101 or xenon lamp 103, in a direction of the optical axis of the imaging optical system 120. The LCD 109 displays a fixation target (not illustrated) for fixing the eye E.
The illumination diaphragm 110 is a diaphragm member to shut out part of the illumination light in order to prevent flare and the like. This illumination diaphragm 110 is configured so as to be movable in the optical axis direction of the illumination optical system 100, and is thus capable of changing an illumination region of the fundus oculi Ef.
The aperture mirror 112 is an optical element that combines the optical axis of the illumination optical system 100 and the optical axis of the imaging optical system 120. In the center region of the aperture mirror 112, an aperture 112a is opened. The optical axis of the illumination optical system 100 and the optical axis of the imaging optical system 120 cross each other at a substantially central position of the aperture 112a. The objective lens 113 is installed in the objective lens part 8a of the main body part 8.
The illumination optical system 100 having such a configuration illuminates the fundus oculi Ef in the following manner. First, at the time of fundus oculi observation, the halogen lamp 101 is turned on and an observation illumination light is emitted. This observation illumination light is applied to the ring transparent plate 107 through the condenser lenses 102 and 104. The light passed through the ring transparent part 107a of the ring transparent plate 107 is reflected by the mirror 108 and, after passing through the LCD 109, the illumination diaphragm 110 and the relay lens 111, is reflected by the aperture mirror 112 so as to be along the optical axis direction of the imaging optical system 120. Then, the light is converged by the objective lens 113 to enter the eye E, thereby illuminating the fundus oculi Ef.
At this moment, since the ring transparent plate 107 is placed in a conjugating position with the pupil of the eye E, a ring-shaped image of the observation illumination light entering the eye E is formed on the pupil. The entering fundus oculi reflection light of the entered observation illumination light is emitted from the eye E through a central dark part of the ring-shaped image on the pupil.
On the other hand, at the time of imaging of the fundus oculi Ef, flush light is emitted from the xenon lamp 103, and the imaging illumination light is applied to the fundus oculi Ef through the same path. In the case of fluorography, either the exciter filter 105 or the exciter filter 106 is selectively placed on the optical path, depending on whether FAG imaging or ICG imaging is carried out.
The imaging optical system 120 comprises: an objective lens 113; an aperture mirror 112 (an aperture 112a thereof); an imaging diaphragm 121; barrier filters 122 and 123; a variable magnifying lens 124; a relay lens 125; an imaging lens 126; a quick return mirror 127; and an imaging media 9a. Herein, the imaging media 9a is an imaging media (a CCD, camera film, instant film or the like) for the still camera 9.
The fundus oculi reflection light of the illumination light exiting through the central dark part of the ring-shaped image formed on the pupil of the eye E enters the imaging diaphragm 121 through the aperture 112a of the aperture mirror 112. The aperture mirror 112 reflects cornea reflection light of the illumination light, and acts so as not to mix the cornea reflection light into the fundus oculi reflection light entering the imaging diaphragm 121. Consequently, generation of flare in observation images and photographed images is inhibited.
The imaging diaphragm 121 is a plate-shaped member having a plurality of circular light-transmitting parts of different sizes. The plurality of light-transmitting parts compose diaphragms with different diaphragm values (F values), and are placed alternatively on the optical path by a drive mechanism (not illustrated).
The barrier filters 122 and 123 can be inserted into and removed from the optical path by a drive mechanism such as a solenoid. In FAG imaging, the barrier filter 122 is placed on the optical path, whereas in ICG imaging, the barrier filter 123 is placed on the optical path. Further, at the time of color-imaging, both the barrier filters 122 and 123 are retracted from the optical path.
The variable magnifying lens 124 is movable in the optical axis direction of the imaging optical system 120 by a drive mechanism (not illustrated). This makes it possible to change an observation magnification and an imaging magnification, and to focus images of the fundus oculi. The imaging lens 126 is a lens that focuses the fundus oculi reflection light from the eye E onto the imaging media 9a. 
The quick return mirror 127 is disposed so as to be capable of being rotated around a rotary shaft 127a by a drive mechanism (not illustrated). In a case where imaging of the fundus oculi Ef is performed with the still camera 9, the fundus oculi reflection light is guided to the imaging media 9a by springing up the quick return mirror 127 that is obliquely mounted on the optical path. Meanwhile, in a case where imaging of the fundus oculi is performed with the imaging device 10, or in a case where observation of the fundus oculi is performed with the naked eye of the examiner, the quick return mirror 127 is obliquely mounted on the optical path to upwardly reflect the fundus oculi reflection light.
The imaging optical system 120 is further provided with, for guiding the fundus oculi reflection light reflected by the quick return mirror 127, a field lens 128, a switching mirror 129, an eyepiece 130, a relay lens 131, a reflection mirror 132, an imaging lens 133, and an image pick-up element 10a. The image pick-up element 10a is an image pick-up element such as a CCD installed in the imaging device 10. On the touch panel monitor 11, a fundus oculi image Ef′ imaged by the image pick-up element 10a is displayed.
The switching mirror 129 is rotatable around a rotary shaft 129a in the same manner as the quick return mirror 127. This switching mirror 129 is obliquely disposed on the optical path during observation with the naked eye, thereby reflecting and guiding the fundus oculi reflection light to the eyepiece 130.
In the case of imaging of a fundus oculi image by the imaging device 10, the switching mirror 129 is retracted from the optical path. The fundus oculi reflection light is focused on the image pick-up element 10a via the relay lens 131, the mirror 132 and the imaging lens 133, and the fundus oculi image Ef′ is displayed on the touch panel monitor 11.
The retinal camera 1000 is a fundus oculi observation device used for observing the surface of the fundus oculi Ef, namely, the surface of the retina. On the other hand, layers such as a photoreceptor layer and a retinal pigment epithelium layer are present in a deep part of the retina, and moreover, organs such as choroidea and sclera are present in a deeper part. Recently, a device for observing these deep tissues has been practically implemented (refer to Japanese Unexamined Patent Application Publications Nos. JP-A 2003-000543, JP-A 2005-241464 and JP-A 2004-502483).
Each of the fundus oculi observation devices disclosed in JP-A 2003-000543, JP-A 2005-241464 and JP-A 2004-502483 is a device to which a so-called OCT (Optical Coherence Tomography) technology is applied (referred to as an optical image measurement device, an optical coherence tomography device, and the like). Such a fundus oculi observation device is a device that splits low-coherence light into two, guides one (signal light) of the lights to the fundus oculi and the other (reference light) to a given reference object and, based on interference light obtained by superimposing the signal light passed through the fundus oculi and the reference light reflected by the reference object, forms tomographic images of the surface and deep layer tissue of the fundus oculi.
The fundus oculi observation device disclosed in JP-A 2004-502483 has a function of presenting the thickness of a layer of the fundus oculi in a quadrant. The thickness of a layer of the fundus oculi is regarded as important information in diagnosis of glaucoma and the like.
For evaluation of the thickness of a layer of the fundus oculi, it is carried out in common to measure the thickness of the layer by setting circular measurement lines on the fundus oculi as shown in FIG. 17 and analyzing tomographic images along the respective measurement lines. Circular measurement lines M1, M2 and M3 have radii of m1, m2 and m3, respectively. The radii m1, m2 and m3 are set to, for example, 1.2 mm, 1.6 mm and 2.0 mm, respectively. The measurement lines M1, M2 and M3 are set concentrically, and a center C thereof is set to the center position of the optic papilla.
In this evaluation of the thickness of a layer of the fundus oculi, a measurement error resulting from the ocular optical system of an eye may occur. Influences of the ocular optical system on a light applied to the fundus oculi are different depending on eyes, but in the conventional way, the measurement lines M1, M2 and M3 are set regardless of the differences among individuals. Therefore, it has been difficult to set the positions of the radii m1, m2 and m3 from the center C of the optic papilla at proper positions, namely, accurately set.
In the conventional way, the measurement lines M1, M2 and M3 are set as described below. First, the refractive power and axial length of the ocular optical system of an eye are measured in advance. Next, the corneal curvature of the eye is estimated by using the result of the measurement and the refractive power of the lens of the Gullstrand's eye model. Subsequently, the magnification of the ocular optical system is calculated by using the estimated value and so on. Then, the radii m1, m2 and m3 are determined by using the value of the magnification, and the measurement lines M1, M2 and M3 are set.
However, since this method employs a standard value based on the eye model, it has been difficult to accurately obtain the magnification of the eye. Therefore, it has been difficult to set the measurement lines M1, M2 and M3 at proper positions with respect to the eye.
An influence of the magnification of the ocular optical system exists at all times when the position and distance on the fundus oculi are considered, not only when the thickness of the layer of the fundus oculi is evaluated.